This project deals with pepsinogens, pepsins, activation peptides and the development of a carboxyl terminal sequencing method. To contribute to understanding of gastric proteases, for formation from zymogens, the properties and the enzymic action of mammalian and lower vertebrate pepsins will be studied. The pepsin inhibiting action of the peptides removed from pepsinogens during activation of several species will be compared. Chemical modification and synthesis of peptides will be directed toward preparing more potent inhibitors as a basis for synthesis of compounds for ulcer therapy. Other physiological roles of the peptides will be investigated. Studies will be continued on a solid phase method for peptide sequencing from the carboxyl terminus in order to develop a quantitative and sensitive method suitable for automation.